1. Field
The present disclosure relates generally to audio systems, and more specifically, to a system and method of reducing power consumption in an audio system by adjusting the power supplied to an audio power amplifier based on the volume level indicated by a volume control module and/or the envelope of the input audio signal.
2. Background
The output of a typical audio system consists of a digital section followed by an analog section. For example, the digital section may include a digital signal processor (DSP) adapted to receive an input digital audio signal, and apply some predetermined signal processing upon the input digital signal. The output of the digital section is coupled to the input of the analog section. The analog section may include a digital-to-analog converter (DAC) adapted to convert the digital audio signal received from the digital section into an analog audio signal. The analog section may also include a power amplifier (PA), such as a class A, A/B, D, E or G power amplifier, adapted to increase the power level of the analog audio signal to sufficiently drive a speaker. This is explained in more detail with reference to the following example.
FIG. 1A illustrates a block diagram of an exemplary conventional audio system 100. In this example, the audio system 100 is configured to generate a stereo output. The left channel section of the stereo output includes a DSP 102-L adapted to receive a left-channel N-bit input audio digital signal and perform some predetermined signal processing upon the signal, a DAC 104-L adapted to convert the digital audio signal received from the DSP 102-L into an analog audio signal, and a power amplifier (PA) 106-L adapted to increase the power level of the analog audio signal to sufficiently drive a left-channel speaker 108-L. The right-channel section of the stereo output includes a DSP 102-R, a DAC 104-R, and a power amplifier (PA) 106-R, and may be configured similar to the left-channel section, except that it acts upon a right-channel N-bit input digital audio signal to generate an analog audio signal with sufficient power to drive a right-channel speaker 108-R.
Generally, the power supply for the digital section is configured differently than the power supply for the analog section. For example, the power supply for the digital section may produce a relatively low supply voltage of approximately 1.2 Volts. Whereas, the power supply for the analog section may produce a higher supply voltage of approximately 3.3 Volts. Both supply voltages are generally fixed. The analog power supply is typically configured to provide power to the analog section such that the analog section can support the maximum audio signal amplitude. However, the analog signal amplitude is usually not at its maximum amplitude. Accordingly, this results in inefficiency in the power used by the audio system 100. This is explained in more detail with reference to the following example.
FIG. 1B illustrates a block diagram of the left-channel of the conventional audio system 100, as discussed above. Additionally, in this diagram, a power supply 110 for supplying power to the digital section, DSP 102-L, is shown. Also, a power supply 112 for supplying power to the analog section, DAC 104-L and power amplifier (PA) 106-L, is shown. As discussed above, the power supply 112 is configured to provide sufficient power to the DAC 104-L and power amplifier 106-L such that these devices can handle the maximum audio signal amplitude. Further, the bias currents for these devices are typically chosen for worst case scenario.
This results in inefficiency in the power consumed by the audio system 100 if the analog section is supporting an audio signal with an amplitude less than the maximum supported amplitude. For instance, this is true if the volume control of the audio system 100 is set to lower than the maximum volume. Additionally, since many audio content, such as music, have moments of high and low signal amplitude, the efficiency of the power consumed by the audio system 100 is lower at low audio signal amplitude.